1. Field of the Invention
The present invention is broadly concerned with compositions and methods for sorbing and/or destroying dangerous substances such as chemical and biological warfare agents. The methods of the invention are carried out by simply contacting the target substance with particulate metal oxide compositions. These compositions can be unmodified, or alternately, the particulate metal oxides can be coated with a second metal oxide, have reactive atoms or mixtures of reactive atoms stabilized on their surfaces, or have species adsorbed on their surfaces. In another embodiment, the particulate metal oxides (unmodified or modified) can be pressed to form pellets which possess the same destructive abilities as the metal oxides in powder form. Methods in accordance with the invention require the use of minimal liquids, thus resulting in very little effluent. Furthermore, the particulate metal oxide compositions utilized in the methods of the invention are not harmful to equipment or to humans and can easily be used directly at the site of contamination.
2. Description of the Prior Art
The threat of biological and chemical warfare has grown considerably in recent times. Numerous countries are capable of developing deadly biological and chemical weapons. Some potent biological agents include the following: bacteria such as Bacillus anthracis (anthrax) and Yersinia pestis (plague); viruses such as variola virus (small pox) and flaviviruses (hemorrhagic fevers); and toxins such as botulinum toxins and saxitoxin. Some potent chemical agents include: blister or vesicant agents such as mustard agents; nerve agents such as methylphosphonothiolate (VX); lung damaging or choking agents such as phosgene (CG); cyanogen agents such as hydrogen cyanide; incapacitants such as 3-quinuclidinyl benzilate; riot control agents such as CS (malonitrile); smokes such as zinc chloride smokes; and some herbicides such as 2,4-D (2,4-dichlorophenoxy acetic acid).
All of the above agents, as well as numerous other biological and chemical agents, pose a significant risk to private citizens as well as to military personnel. For example, vesicant agents bum and blister the skin or any other part of the body they contact, including eyes, mucus membranes, lungs, and skin. Nerve agents are particularly toxic and are generally colorless, odorless, and readily absorbable through the lungs, eyes, skin, and intestinal track. Even a brief exposure can be fatal and death can occur in as quickly as 1 to 10 minutes. Biological agents such as anthrax are easily disseminated as aerosols and thus have the ability to inflict a large number of casualties over a wide area with minimal logistical requirements. Many biological agents are highly stable and thus can persist for long periods of time in soil or food.
There are currently two general types of decontamination methods for biological agents: chemical disinfection and physical decontamination. Chemical disinfectants, such as hypochlorite solutions, are useful but are corrosive to most metals and fabrics, as well as to human skin. Physical decontamination, on the other hand, usually involves dry heat up to 160xc2x0 C. for 2 hours, or steam or super-heated steam for about 20 minutes. Sometimes UV light can be used effectively, but it is difficult to develop and standardize for practical use.
These methods have many drawbacks. The use of chemical disinfectants can be harmful to personnel and equipment due to the corrosiveness and toxicity of the disinfectants. Furthermore, chemical disinfectants result in large quantities of effluent which must be disposed of in an environmentally sound manner. Physical decontamination methods are lacking because they require large expenditures of energy. Both chemical and physical methods are difficult to use directly at the contaminated site due to bulky equipment and/or large quantities of liquids which must be transported to the site. Finally, while a particular decontamination or disinfection method may be suitable for biological decontamination, it is generally not effective against chemical agents. There is a need for decontamination compounds which are effective against a wide variety of both chemical and biological agents, have low energy requirements, are easily transportable, do not harm skin or equipment, and employ small amounts of liquids with minimal or no effluent.
The present invention overcomes these problems and provides compositions and methods for sorbing (e.g., adsorption and chemisorption) and destroying biological and chemical agents. To this end, the invention contemplates the use of finely divided nanoscale metal oxide adsorbents. These adsorbents can be used in an unmodified form or can be pelletized, coated with a second metal oxide, or have reactive atoms stabilized on their surfaces. These decontamination reactions can be carried out over a wide range of temperatures and can be conducted at the contaminated site. Furthermore, these adsorbents are not harmful to equipment or to humans.
In more detail, the nanoscale adsorbents used in the methods of the invention are formed from metal oxides selected from the group consisting of MgO, CaO, TiO2, ZrO2, FeO, V2O3, V2O5, Mn2O3, Fe2O3, NiO, CuO, Al2O3, ZnO, and mixtures thereof. While conventionally prepared powders can be used in the methods of the invention, the preferred powders are prepared by aerogel techniques from Utamapanya et al., Chem. Mater., 3:175-181 (1991), incorporated by reference herein. The adsorbents should have an average crystallite size of up to about 20 nm, preferably from about 3-8 nm, and more preferably 4 nm, and exhibit a Brunauer-Emmett-Teller (BET) multi-point surface area of at least about 15 m2/g, preferably at least about 200 m2/g, and more preferably about 400 m2/g. In terms of pore radius, the preferred adsorbents should have an average pore radius of at least about 45 xc3x85, more preferably from about 50-100 xc3x85, and most preferably from about 60-75 xc3x85.
These nanoscale adsorbents can be used alone and in their powder form, or they can be modified. For example, the finely divided particles of the metal oxides can have at least a portion of their surfaces coated with a quantity of a second metal oxide different than the first metal oxide and selected from oxides of metals selected from the group consisting of Ti, V, Fe, Cu, Ni, Co, Mn, Zn and mixtures thereof In preferred forms, the coated metal oxide particles comprise a first metal oxide selected from the group consisting of MgO and CaO, whereas the second metal oxide is preferably Fe2O3. For most efficient uses, the particles of the first metal oxide should have the average crystallite sizes and multi-point surface areas set forth above. As is conventional in the art, the term xe2x80x9cparticlesxe2x80x9d is used herein interchangeably with the term xe2x80x9ccrystallite.xe2x80x9d The second metal oxide should be in the form of an extremely thin layer or coating applied onto the surface of the first metal oxide, thus giving an average overall size for the composite of up to about 21 nm, more preferably from about 5-11 nm, and most preferably about 5 nm. Generally, the first metal oxide should be present in substantial excess relative to the second metal oxide. Thus, the first metal oxide comprises from about 90-99% by weight of the total composite material, and more preferably from about 95-99% by weight. Correspondingly, the second metal oxide should comprise from 1-10% by weight of the total composite, and more preferably from about 1-5% by weight. At least 75% of the surface area of the first metal oxide particles should be covered with the second oxide, and more preferably from about 90-100% of this surface area should be covered.
The coated metal oxide particles or crystallites of this embodiment are preferably fabricated by first forming the very finely divided first particulate material using known aerogel techniques. Thereafter, the second material is applied onto the surface of the first metal oxide as an extremely thin layer, e.g., a monolayer having a thickness on the order of less than 1 nm. For example, nanocrystalline MgO can be prepared and then treated with an iron salt such as iron III (acetylacetonate)3 with the ligands being driven off by heating.
In another embodiment, the methods of the invention utilize particulate metal oxides having reactive atoms (different from those atoms making up the metal oxide) stabilized on the surfaces thereof. In more detail, the metal oxide particulates have oxygen ion moieties on their surfaces with reactive atoms interacted or chemisorbed with those surface oxygen ions. The metal oxide particles are, as with the two previously described embodiments, selected from the group consisting of MgO, CaO, TiO2, ZrO2, FeO, V2O3, V2O5, Mn2O3, Fe2O3, NiO, CuO, Al2O3, ZnO, and mixtures thereof. Furthermore, the particles should have the same average crystallite sizes and surface areas described above. Preferably, the reactive atoms utilized in this embodiment are selected from the group consisting of halogens and Group I metals. When halogens are the reactive atoms being stabilized on the surfaces of the particles, the atoms can be atoms of the same halogen (e.g., only chlorine atoms), or the atoms can be mixtures of atoms of different halogens (e.g., both chlorine and bromine atoms on the metal oxide surfaces). When stabilizing a Group I metal atom, the atom loading on the metal oxide should be from about 5-40% by weight, preferably from about 10-15% by weight, and more preferably about 12% by weight, based upon the weight of the atom-loaded metal oxide taken as 100%. When stabilizing either a Group I metal atom or a halogen atom, the atom loading on the metal oxide can also be expressed as a concentration of atoms per unit of surface area of the metal oxide, i.e., at least about 2 atoms per square nanometer of metal oxide surface area, preferably from about 3-8 atoms per square nanometer of metal oxide surface area, and more preferably from about 4-5 atoms per square nanometer of metal oxide surface area. The preferred Group I metal is potassium, and the preferred halogens are chlorine and bromine.
The surface-stabilized, reactive atom composites are formed by heating a quantity of particulate metal oxide particles to a temperature of at least about 200xc2x0 C., preferably at least about 300xc2x0 C., and more preferably to a level of from about 450 to about 500xc2x0 C. Heating the metal oxide particles to these temperatures removes water from the particles so that the final compositions have a surface hydroxyl concentration of less than about 5 hydroxyl groups per square nanometer of metal oxide surface area, and preferably less than about 4 hydroxyl groups per square nanometer of metal oxide surface area. The particles are preferably allowed to cool to room temperature. The particles are then contacted with a source of reactive atoms, e.g., a compound which dissociates into reactive atoms under the proper reaction conditions. The reactive atoms interact with the metal oxide surface oxygen ions, thus stabilizing the atoms on the oxide surface. As used hereinafter, the terms xe2x80x9cstabilizedxe2x80x9d and xe2x80x9cstablexe2x80x9d mean that, when the metal oxide-atom adducts are heated to a temperature of about 100xc2x0 C., less than about 10% of the total weight loss of the adduct is attributable to the reactive atoms desorbing.
In another embodiment, the methods of the invention utilize particulate metal oxides having species different than the metal oxide adsorbed on the surfaces thereof The metal oxide particles are selected from the group consisting of MgO, CaO, TiO2, ZrO2, FeO, V2O3, V2O5, Mn2O3, Fe2O3, NiO, CuO, Al2O3, ZnO, and mixtures thereof. The particles should have the same average crystallite sizes and surface areas described above. Preferably, the adsorbed species are selected from the group consisting of oxides of Group V elements, oxides of Group VI elements, and ozone. Preferred oxides of Group V and VI elements are NO2 and SO2, respectively. When adsorbing a species on the metal oxide surfaces, the species loading on the metal oxide should be from about 1-60% by weight, preferably from about 5-40% by weight, and more preferably about 15-25% by weight, based upon the weight of the adsorbed species-metal oxide taken as 100%. The species loading can also be expressed as a concentration of species molecules per unit of surface area of metal oxide. Preferably, there are at least about 2 molecules of the species adsorbed per square nanometer of metal oxide and more preferably at least about 5 molecules. The adsorbed-species, metal oxide composites are formed by contacting a quantity of the desired metal oxide (in an air evacuated flask) with the gaseous species. The sample is allowed to react for about 30 minutes, after which time the excess gaseous species is pumped out.
In yet another embodiment, the methods of the invention contemplate forming the above metal oxide particles and composites including those particles (i.e., unmodified, finely divided metal oxide particles, finely divided metal oxide particles coated with a second metal oxide, finely divided metal oxide particles having reactive atoms and mixtures of reactive atoms stabilized on the surfaces thereof, and metal oxide particles having species adsorbed on the surfaces thereof) into pellets for use when powdered decontaminants are not feasible. These pellets are formed by pressing a quantity of one of these powdered metal oxide composites at a pressure of from about 50-6,000 psi, more preferably from about 500-5000 psi, and most preferably at about 2,000 psi. While pressures are typically applied to the powder by way of an automatic or hydraulic press, one skilled in the art will appreciate that the pellets can be formed by any pressure-applying means. Furthermore, a binder or filler can be mixed with the adsorbent powder and the pellets can be formed by pressing the mixture by hand. Agglomerating or agglomerated as used hereinafter includes pressing together of the adsorbent powder as well as pressed-together adsorbent powder. Agglomerating also includes the spraying or pressing of the adsorbent powder (either alone or in a mixture) around a core material other than the adsorbent powder.
In order to effectively carry out the methods of the invention, the pellets should retain at least about 25% of the multi-point surface area/unit mass of the metal hydroxide or metal oxide (whichever was used to form the pellet) particles prior to pressing together thereof. More preferably, the multi-point surface area/unit mass of the pellets will be at least about 50%, and most preferably at least about 90%, of the multi-point surface area/unit mass of the starting metal oxide or metal hydroxide particles prior to pressing. The pellets should retain at least about 25% of the total pore volume of the metal hydroxide or metal oxide particles prior to pressing thereof, more preferably, at least about 50%, and most preferably at least about 90% thereof. In the most preferred forms, the pellets will retain the above percentages of both the multi-point surface area/unit mass and the total pore volume. The pellets normally have a density of from about 0.2 to about 2.0 g/cm3, more preferably from about 0.3 to about 1.0 g/cm3, and most preferably from about 0.4 to about 0.7 g/cm3. The minimum surface-to-surface dimension of the pellets (e.g., diameter in the case of spherical or elongated pellet bodies) is at least about 1 mm, more preferably from about 10-20 mm.
In carrying out the methods of the invention, one or more of the above described metal oxide particle composites are contacted with the target substance to be sorbed, decontaminated or destroyed under conditions for sorbing, decontaminating or destroying at least a portion of the substance. The methods of the invention provide for destructively adsorbing a wide variety of chemical agents, including agents selected from the group consisting of acids, alcohols, compounds having an atom of P, S, N, Se, or Te, hydrocarbon compounds, and toxic metal compounds. The methods of the invention also provide for biocidally adsorbing a wide variety of biological agents, including bacteria, fungi, viruses, rickettsiae, chlamydia, and toxins. Utilizing the metal oxide particulate composites in accordance with the methods of the invention is particularly useful for biocidally adsorbing biological agents such as bacteria, especially gram positive bacteria like B. globigii and B. cereus. The composites are also useful for adsorbing toxins such as Aflatoxins, Botulinum toxins, Clostridium perfringens toxins, Conotoxins, Ricins, Saxitoxins, Shiga toxins, Staphylococcus aureus toxins, Tetrodotoxins, Verotoxins, Microcystins (Cyanginosin), Abrins, Cholera toxins, Tetanus toxins, Trichothecene mycotoxins, Modeccins, Volkensins, Viscum Album Lectin 1, Streptococcal toxins (e.g., erythrogenic toxin and streptolysins), Pseudomonas A toxins, Diphtheria toxins, Listeria monocytogenes toxins, Bacillus anthracis toxic complexes, Francisella tularensis toxins, whooping cough pertussis toxins, Yersiniapestis toxic complexes, Yersinia enterocolytica enterotoxins, and Pasteurella toxins. In another embodiment, the methods of the invention provide for the destructive adsorption of hydrocarbon compounds, both chlorinated and non-chlorinated.
The contacting step can take place over a wide range of temperatures and pressures. For example, the particulate metal oxide composites can be taken directly to a contaminated site and contacted with the contaminant and/or contaminated surfaces at ambient temperatures and pressures. Alternately, the contacting step can be carried out at a temperature of from about xe2x88x9240-600xc2x0 C. If the contacting step is to be carried out under ambient temperatures, preferably the reaction temperature range is from about 10-200xc2x0 C. If the contacting step is to be carried out under high temperature conditions, then preferably the temperature range for the reaction is from about 350-550xc2x0 C.
If the contacting step is carried out under ambient conditions, the particulate metal oxide composites should be allowed to contact the target substance for at least about 0.5 minutes, preferably from about 1-100 minutes, and more preferably from about 1.5-20 minutes. If the contacting step is carried out under high temperatures conditions, then the particulate metal oxide composites should be allowed to contact the target substance for at least about 4 seconds, preferably for about 5-20 seconds, and more preferably for about 5-10 seconds.
If the target substance is a biological agent, the contacting step results in at least about a 90% reduction in the viable units of the biological agent, preferably at least about a 95% reduction, and more preferably at least about a 98% reduction. If the target substance is a chemical agent, the contacting step results in at least about 90% reduction in the concentration of the chemical agent, preferably at least about a 95% reduction, and more preferably at least about a 99% reduction.
Those skilled in the art will appreciate the benefits provided by the methods of the invention. In accordance with the invention, military personnel can utilize the particulate metal oxides and composites thereof to neutralize highly toxic substances such as nerve agents and biological agents. These particles and composites can be utilized in their non-toxic ultrafine powder form to decontaminate areas exposed to these agents, or the highly pelletized composites can be utilized in air purification or water filtration devices. Other countermeasure and protective uses for the metal oxide particles and composites of the particles include personnel ventilation systems and wide-area surface decontamination. Furthermore, the metal oxide composites remain airborne for at least one hour, thus providing effective airborne decontamination of chemical or biological agents. Alternately, the composites can be formulated into a cream or incorporated in or on clothing in order to provide protection to personnel at risk of contacting a dangerous agent.
Unlike currently available decontamination methods, the methods of the invention utilize composites that are non-toxic to humans and non-corrosive to equipment, thus permitting the decontaminated equipment to be put back into use rather than discarded. Furthermore, because the composites are easy to disperse and readily transportable, and because little or no water is required to practice the invention, it is relatively simple to destroy the contaminants at the contaminated site.